Study On Trust Models For P2P Systems

P2P service has become one of the most important and popular applications in the Internet nowadays. However, the nature of openness, anonymity and loose-coupling relationship among peers in P2P systems make it an ideal environment for malicious users to spread unsolicited and harmful content, opening the door to abuses of the networks. Moreover, high dynamics of peer behaviors always bring on unsteadiness of the network bandwidth and performance, the quality of service (QoS) of the P2P systems can't be guaranteed. Therefore, it is necessary to construct trust relationships among peers in distributed large-scale P2P systems.Trust represents an integrated evaluation of behavior and capacity of a peer from the viewpoint of another peer. Trustworthiness among peers in P2P systems can incent peers to cooperate and share the network resources. Current researches on trust mostly focus on setting up the reliable trust management model for P2P systems. In this thesis, we stydy the trust models of P2P systems. The main achievements are as follows:An important challenge to evaluate peer's trust in P2P systems is how to cope with dishonest recommendations of malicious efficiently. However, the existing trust models do not provide adequate support to cope with this problem. We presents a dynamic trust model for P2P systems based on recommendation credibility measure, which aims to differentiate honest and dishonest recommendation. The evaluation of recommending peers' credibility is introduced into the trust model. For the trust evaluation of node in the P2P systems, the weight of the peer's trust evaluation can be dynamically adjusted in interactions and the credibility of each responding peer's recommendation can be measured in order to filter the noise of low credible peers and thus more exact and objective values of trust evaluation can be achieved. The theoretical analysis and simulation results show that this presented trust model has the advantages of modeling dynamic trust relationship and aggregating recommendation information over to the existing trust models, and it can improve remarkably the accuracy of trust evaluation and segregate the attack of dishonest or malicious peers. The model can effectively construct a high efficient and reliable trust relationship among peers, prevent malicious attack and enhance security and efficiency of P2P systems.A novel multi-grain management trust model is also proposed. This trust model applies the advantages of trust mechanism in the real-life world, evaluates peer's trust in quantitative mothod, and incorporates most concepts that are essential to determine trust-based decisions. Method of aggregation of trust evaluation is proposed in the trust model. The credibility of each responding peer's recommendation can be measu red byits similarity, activity, popularity and cooperation between peers. The presented model can filter noise in responses and obtain more accurate and objective trust values.